1. Field of the Invention
The present invention relates to an exposure apparatus and a device manufacturing method.
2. Description of the Related Art
Along with the recent increase in the degree of integration of semiconductor devices, higher resolving powers are demanded of semiconductor exposure apparatuses. To increase the resolving power, a projection optical system needs to have an NA equal to or higher than 0.9 to result in a further increase in the size of the projection optical system.
FIG. 4 is a schematic view showing the arrangement of an exposure apparatus described in Japanese Patent Laid-Open No. 11-297587. To reduce vibration, active mounts 12 including actuators support a barrel support (projection optical system support) 10 supporting a projection optical system 9. A Z interferometer 16 and X-Y interferometer 17 for measuring the position of a wafer stage 7 supporting a wafer 6 are attached to the barrel support 10. The interferometers 16 and 17 measure the position of the wafer stage 7 relative to the projection optical system 9 to align the wafer stage 7 based on this measurement result.
When the interferometers 16 and 17 are attached to the barrel support 10 in the above-described way, measurement errors occur upon deformation of the barrel support 10. The barrel support 10 may deform not only when the actuator of the active mount 12 generates heat but also when a heavy structure is mounted on the barrel support 10. In particular, upon mounting a relatively heavy projection optical system 9, the barrel support 10 may significantly deform.
As a measure against such deformation, the barrel support 10 may be made of a low-thermal-expansive material or may be increased in size. However, the former measure is disadvantageous from the viewpoint of cost, while the latter measure increases the size of the whole apparatus and requires a long time to manufacture the barrel support 10.